The Build Refinement, Voxel command is designed to quickly create voxel refinement blocks used as background blocks in overset grid
topologies. Please refer to the Grid, Overset command, for more information regarding overset
The selected entities will be queried for grid spacings which in turn can be used to determine a homogeneous spacing for the new voxel block. Refer to
the Spacing Controls section below for more information on setting spacings. Note that the selected entities are not used to form the faces of the
new block; only their spacings are used for reference.
Voxel blocks are composed of hierarchical Cartesian cells which are clustered about and sized by the selected entities. Root voxel cell sizes are
specified for the rectangular block and recursively subdivided based on the size field determined from the selected
grid entities and any sources located inside a region computed as twice the size of the block's extent box. Subdivision stops when the voxel cell sizes match
the local size field. Transitions between levels in the Cartesian mesh are made using tetrahedral cells and pyramids in order to maintain point-to-point cell
face matching. Users can override the default minimum and maximum cell edge sizes and set a minimum number of cell transition layers using the tools in this
Use the Build Refinement command to create block topology quickly based on existing grid entities.
At the top of the Build Refinement panel, you will find a table displaying the X, Y, and Z Characteristic Length
of the selected entities. Additionally, the Minimum, Average, and Maximum spacings of the size field and the actual boundaries of
the new block are shown. Keep in mind that the size field is computed considering the initial selected entities, any
enabled sources, and any additional grid entities marked as size field influencers in
the Size Field tab.
The Block Type frame (shown above with the Voxel option circled in red) allows you to choose the block type to be
created: Structured, Unstructured, or Voxel. When you enter the Build Refinement panel for the first time, the Block
Type will be selected directly via the menu.
In the Shape frame (shown below), you can set up a symmetry plane definition for the new block as well as its extents. By default for Symmetry
Planes, the Automatic toggle is checked on. This means that the command will try to determine a single or two planes of symmetry
automatically from the selected grid entities. If a symmetry plane is not detected automatically, you can use the first and second pull-down lists
to select it manually. Note that using one of the two pull-down lists will uncheck the Automatic toggle automatically. You can recheck this toggle to
have the panel restore the automatically detected symmetry plane(s).
In the Margins frame, you will find fields to set the extents of the new block in the X, Y, and Z coordinates. The Uniform text field
allows you to enter a single number which will be used in all three coordinate directions. This value will automatically populate the individual coordinate
direction fields just below (i.e. +X, -X, +Y, -Y, +Z, and -Z). The individual fields can also be used to
enter unique numerical values for each coordinate minimum and maximum.
Use the Shape frame to specify the extents of the new block.
The default Min. Edge and Max. Edge for voxel cells can be changed directly by unchecking Use Default and entering a new value in
the corresponding text fields. These values are absolute limiters. Therefore if there is an influence domain selected for the construction of this block type,
and that domain has cell edges smaller than the Min. Edge specified, the Min. Edge value is used.
The Transition Layers parameter is a target for the number of layers of equally-sized (i.e. isotropic) hexahedral cells placed between two consecutive
transition layers in a voxel block. Note that the transition layers contain a combination of pyramid and tetrahedral volume cells. The default value for this
parameter, when Use Default is checked on, is 3.
Use the Voxel frame to specify voxel edge and transition layer attributes for the new block.
Finally, you can click Update Grid Entities at the bottom of the panel to preview the bounding domains of the pending new block. If size field
refinement or boundary adaption will be necessary, the Solve command for
voxel blocks will need to be used. If desired, tools in the collapsed Selection frame will provide a selection mode to reselect the domains to
be used by the new block. This would be equivalent to clicking Cancel to exit the command, changing your selection, and entering Build
Use the Update Grid Entities command to preview the pending block boundaries. Additionally, use the commands in the Selection frame to update your initial
When the new block is complete, click OK to save it and close the panel, click Cancel to discard it and close the panel, or
click Apply to save it and continue on to creating another block.